Activated carbon, a widely used carbonaceous adsorbent, has large specific surface area and a relatively large pore size. This requires control of the size and the distribution of pores by a thermal decomposition method, an activation method, a thermal modification method, etc. Another problem is that having various surface functional groups and low crystallinity, activated carbon is significantly degraded when reproduced.
In addition to carbonaceous adsorbents, zeolite, for example, is known, which has pores of molecular size and has a molecular sieve effect. However, the disadvantage of zeolite is its poor chemical stability as it is degraded by strong acid and strong alkali and its heavy weight because of the high density.
A carbon nanohorn aggregate is an aggregate in which a tubular structure made of a six-membered carbon ring with a diameter of 2 to 5 nm and a length of 40 to 50 nm is radially aggregated, and is an excellent adsorption material which has large specific surface area, uniform pores and high crystallinity (Patent Literature 1, Patent Literature 2). For this reason, the aggregate is suitable for adsorbing gas such as hydrogen, fluorine, methane, boron and ammonia (Patent Literature 3, Patent Literature 4) and liquid such as water, ethanol, toluene and xylene. Furthermore, having a tubular structure, the carbon nanohorn aggregate is capable of including and releasing various substances (Patent Literature 5). Moreover, due to its aggregate structure, the carbon nanohorn aggregate can be used as a carrier which carries metal, oxide etc. (Patent Literature 6).